Present color broadcasting in Japan and the U.S.A. adopts the NTSC method for executing 2:1 interlaced scanning using 525 scanning lines. On the other hand, a display screen has been wider so that a display screen meets needs for a realistic image with high quality. Accordingly, the wide television signal broadcasting method, which can satisfy both the compatibility with present broadcasting and needs for wider display screen, is suggested. In this method, if, for example, a letter box image is displayed, an effective number of scanning lines is decreased from 480 to 360 per frame, and thus, with non-image portions in top and bottom sections, the image whose aspect ratio becomes 16:9 is displayed. Moreover, in order to improve vertical resolution, components from 360 TVs to 480 TVs should be transmitted as a vertical reinforcing signal particularly in the case of a still picture.
FIG. 11 is a block diagram which shows one section of a typical signal processing method for an EDTV2 signal. The EDTV2 (Extended Definition Television-2) signal is a TV signal for the so-called second generation of "Clear Vision", which is suggested in order to realize display of a wide image with high quality, and a number of scanning lines for 1 field is 180. In the above signal processing method, color signals, etc. of the EDTV2 signal are processed successively in an interlacing-sequential converting circuit 51, a scanning line number converting circuit 52, a matrix circuit 53, a D-A converter 54 and a control circuit 55. Then, the signals are inputted into a scanning electrode driving circuit 56 and a signal electrode driving circuit 57. When driven by these driving circuits 56 and 57, an image based on the EDTV2 signal is displayed on a display 58 having, for example, 240 vertical lines.
In the signal processing method shown in FIG. 11, a number of scanning lines of a video signal is set to 480 (240 per field), and an image is displayed on the display 58. In order to gain a vertical reinforcing signal for increasing the components from 360 TV lines to 480 TV lines, the scanning line number converting circuit 52 is provided, but a lot of line memories and filters are required.
In the case of CRT, as described in Japanese Unexamined Patent Publication No. 7-67051/1995 (Tokukaihei 7-67051), for example, instead of the above processing method, TV signals are discriminated and a deflection angle is controlled. On the other hand, in the case of a liquid crystal display device which is a kind of a matrix-type display device, instead of the above processing method, (1) a calculating circuit having a complicated circuit configuration is provided or (2) as described in Japanese Unexamined Patent Publication No. 7-175451/1995 (Tokukaihei 7-175451), a signal electrode driving circuit which increases a scanning frequency and time-division-drives a signal electrode using a plurality of frames, and a scanning electrode driving circuit which drives a scanning electrode of a liquid crystal display panel are provided.
As mentioned above, in a conventional matrix-type display device, in the case where an image, which is based on a video signal in which a number of scanning lines is smaller than a number of vertical lines of a display screen, is displayed on the whole display screen without a non-image portion, a circuit having a complicated circuit configuration should be provided. Namely, the scanning line number converting circuit 52, the calculating circuit or the circuit having a complicated circuit configuration disclosed in Japanese Unexamined Patent Publication No. 7-175451/1995 (Tokukaihei 7-175451) is required. The provision of such a circuit having a complicated circuit configuration causes a steep rise in costs.
As mentioned above, in the display method in the conventional matrix-type display device, since a lot of hardware and complicated circuits are required, the method has a disadvantage of great cost.